Heat exchanger

ABSTRACT

In order to provide a heat exchanger with casing having a multiplicity of tubes through the interiors of which a high-temperature gas for heating flows, wherein the thermal stress is smoothly accommodated and wherein a fluid to be heated or a heating fluid flows uniformly through the outsides of the tubes, a multiplicity of flat tubes are joined at their opposed ends to a pair of discoidal tube plates, the outer periphery of the flat tubes being enclosed by an inner cylinder having a rectangular cross-section except the opposed end portions of the flat tubes, with a pair of baffle plates being disposed at the opposed ends of the inner cylinder. The pair of baffle plates are covered with an circular outer cylinder having a corrugated portion that is thermally expandable, with an inlet and an outlet for the fluid to be heated or the heating fluid positioned between the pair of baffle plates and the tube plates.

TECHNICAL FIELD

The present invention relates to a heat exchanger for high temperatureused in a fuel cell reformer, etc.

BACKGROUND ART

In a fuel cell using hydrogen and oxygen as its fuel, the hydrogen isgenerated by a reformer in the form of a high-temperature-use heatexchanger. The reformer acts to deliver hydrocarbon such as methanol andsteam into a catalyst and applies thereto external heat to generatehydrogen.

Examples of such a heat exchanger for the reformer include one disclosedin Japanese Patent Application Laid-Open Publication No. 2002-80203.This is arranged such that a multiplicity of juxtaposed flat tubes arejoined at their respective opposed ends to square tube plates in an gastight manner to form a core, with the tube plates in a pair beingconnected to each other by a square-in-section casing. The casing isprovided at peripheries around one end and the other end thereof in thelongitudinal direction, respectively, with an inlet for a reformingmaterial and an outlet for a reforming gas, with an inlet tank and anoutlet tank for a combustion gas being disposed around the peripheriesof the tube plates. A bellows-like square-in-section cylinder isinterposed between the casing and the tube plates so as to relax athermal stress occurring between the tubes and the casing.

Due to its square cross-section, however, the square-in-section ofbellows-like thermal stress relaxation means tend to suffer from adrawback of being hard to smoothly stretch in its axial direction. Inaddition, its fabrication is not easy. Mere forming of a cylindricalcasing would not allow a fluid to be heated to pass uniformly throughparts of the core.

It is therefore the object of the present invention to overcome theabove drawbacks.

DISCLOSURE OF THE INVENTION

The present invention of claim 1 provides a heat exchanger comprising:

a core (4) in the aggregate of a multiplicity of juxtaposed flat tubes(3), with a heating fluid (1) flowing through one of the inside and theoutside of the flat tubes (3), with a fluid to be heated (2) flowingthrough the other;

a pair of discoidal tube plates (5) including tube insertion aperturesto which the flat tubes (3) are jointed at their respective opposedends;

an inner cylinder (6) having a rectangular cross-section enclosing theouter periphery of the core (4) except the vicinities of the pair oftube plates (5);

a first baffle plate (7) having a circular periphery fitted to the outerperiphery at one end of the inner cylinder (6), the first baffle plate(7) confronting one of the pair of tube plates (5);

a circular outer cylinder (10) having one end joined to the first baffleplate (7) and the other end joined to a second baffle plate (8) with acircular periphery disposed on the outer periphery at the other end ofthe inner cylinder (6) or to the other of the pair of tube plates (5),the outer cylinder (10) including on its outer periphery a corrugatedportion that is thermally expandable in the axial direction; and

an outlet (11) and an inlet (12) for the fluid to be heated (2) or theheating fluid (1) disposed at the both end portions of the core (4)between the opposed ends of the inner cylinder (6) and the pair of tubeplates (5), wherein

a lead-in port (13) and a lead-out port (14) for the heating fluid (1)or the fluid to be heated (2) are connected respectively to the pair oftube plates (5).

The present invention of claim 2 provide the heat exchanger of claim 1,wherein

the second baffle plate (8) having the circular outer periphery isfitted at its rectangular inner periphery to the outer periphery at theother end of the inner cylinder (6) in such a manner as to be slightlydisplaceable in the axial direction of the inner cylinder (6)confronting the other of the pair of tube plates (5), wherein

the outer cylinder (10) is firmly connected at the other end thereof tothe outer periphery of the second baffle plate (8), wherein

the first baffle plate (7) is fitted at its rectangular inner peripheryto the outer periphery at one end of the inner cylinder (6) with thefirst baffle plate (7) being secured to the outer cylinder (10), andwherein

the heat exchanger further comprises a first (15) and a second (16)cylindrical tank bodies whose opposed ends are firmly connectedrespectively to the tube plates (5) and to the first (7) and the second(8) baffle plates confronting the tube plates (5).

The heat exchanger of the present invention has the above constitutionand the following advantages. That is, at least one first baffle plate 7is fitted to the outer periphery at one end of the inner cylinder 6,with the outlet 11 and inlet 12 for the fluid to be heated and theheating fluid being positioned between the opposed ends of the innercylinder 6 and the tube plates 5, the outer cylinder 10 being formedinto a circular cylinder with the inner cylinder 6 being of arectangular cross-section that encloses the outer periphery of the core4. The presence of the first baffle plate 7 enables the fluid 2 to beheated or the heating fluid 1 to securely be delivered to the interiorof the inner cylinder 6 to ensure a uniform heat exchange at respectiveparts. The fluid 2 to be heated or the heating fluid 1 can thus beprevented from flowing through the space defined between the inner tube6 and the first baffle plate 7.

Since the outer cylinder 10 is formed into a circular cylinder whoseouter periphery is provided with the corrugated portion 9 that isthermally expandable in the axial direction, its fabrication andexpansion and contraction attendant on the thermal expansion becomeeasy, achieving a high durability.

The second baffle plate 8 is fitted at its rectangular inner peripheryto the inner cylinder 6 such that it is displaceable slightly in theaxial direction with respect to the inner cylinder, whereby theexpansion of the core 4 can more effectively be accommodated by thecorrugated portion 9. This results in a durable heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger of the presentinvention;

FIG. 2 is a partly cut-away exploded explanatory view of the heatexchanger;

FIG. 3 is a longitudinal cross-sectional view of the heat exchanger;

FIG. 4 is a cross-sectional view of the heat exchanger taken along lineIV-IV of FIG. 3; and

FIG. 5 is a longitudinal cross-sectional view of the heat exchanger,showing another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to the drawings.

FIG. 1 is a perspective view of a heat exchanger of the presentinvention, FIG. 2 is an exploded explanatory view of the same, FIG. 3 isa longitudinal cross-sectional view of FIG. 1, and FIG. 4 is across-sectional view taken along line IV-IV of FIG. 3.

The heat exchanger includes a multiplicity of juxtaposed flat tubes 3each having inner fins 17 in its interior, with outer fins 18 carrying acatalyst disposed between the adjacent flat tubes 3, to make up a core 4in the aggregate. The flat tubes 3 are joined at their respectiveopposed ends to tube insertion apertures of a pair of discoidal tubeplates 5 in an gas tight manner.

The outer periphery of the core 4 is covered with a square-in-sectioninner cylinder 6 except the vicinities of the pair of tube plate 5. Theinner cylinder 6 includes two opposed side members having a lengthsmaller than that of the flat tubes 3, and upper and lower plates havinga length substantially equal to that of the flat tubes 3. This allowsboth end portions of the aggregate flat tubes 3 to be exposed at bothextremity sides of the inner cylinder 6. The outer periphery of theinner cylinder 6 is covered with an outer cylinder 10 via a first baffleplate 7 and a second baffle plate in a pair. The outer cylinder 10 isformed into a circular cylinder having at its one end portion in theaxial direction a corrugated portion 9 that is thermally expandable inthe axial direction.

The first baffle plate 7 as shown in FIG. 2 consists of a pair of platehalves 7 a and 7 b that include rectangular openings fitted from bothsides to the side members of the inner cylinder 6 at the end portions ofthe side members, with their joints and the inner cylinder 6 beingfirmly welded together in an gas tight manner as shown in FIG. 3. Theouter periphery of the first baffle plate 7 and the outer cylinder 10 atits one end in the axial direction are firmly welded together in an gastight manner over the entire periphery.

Similar to the first baffle plate 7, the second baffle plate 8 is formedof a two-segmented member whose outer periphery is firmly welded to theother end in the axial direction of the outer cylinder 10 in an gastight manner. Between the rectangular inner periphery thereof and theouter periphery of the inner cylinder 6, however, is formed a slight gapas shown in FIG. 3, that is an unwelded portion 20.

The outer peripheries of the first baffle plate 7 and of the secondbaffle plate 8 and the outer peripheries of the tube plates 5confronting the baffle plates 7 and 8 are then firmly welded to opposedends of a first cylindrical tank 15 and of a second cylindrical tank 16in an gas tight manner. The first tank 15 and the second tank 16 areformed with an outlet 11 and an inlet 12, respectively, as shown inFIG. 1. In this example, a pair of pipes are projectingly provided atthe openings, leading to the interiors of the tanks. To the outerperipheries of the pair of tube plates 5 are joined a lead-in port 13and a lead-out port 14 that are tapered outwardly in the axialdirection, with ducts not shown for a combustion gas being connected tothe extremities of the tapered ports.

In the thus constituted heat exchanger, a heating fluid 1 in the form ofthe combustion gas is introduced into the lead-in port 13 and moves fromright to left through the interiors of the flat tubes 3. The heatingfluid 1 then flows out through the lead-out port 14.

In FIG. 1, a fluid 2 to be heated in the form of a mixture of steam andhydrocarbon is introduced through the inlet 12 into the interior of thesecond tank 16. The fluid 2 to be heated flows through a gap definedbetween the leftward end of the side member and the tube plate 5 intothe interior of the inner tube 6 and then moves from left to right alongthe outer peripheries of the flat tubes 3 and through the interiors ofouter fins 18. The fluid 2 then flows into the interior of the firsttank 15 defined between the first baffle plate 7 and the tube plate 5confronting the plate 7 and is delivered via the outlet 11 to theexterior. A heat exchange is thus achieved between the heating fluid 1and the fluid 2 to be heated, so that the fluid 2 to be heated turns toreformed gas by the action of the catalyst carried on the outer fins 18,which in turn is delivered to a power generating unit of the fuel cell.

At that time, the flat tubes 3 undergo a thermal expansion due to thehigh-temperature heating fluid 1 moving through the interiors of theflat tubes. This allows the corrugated portion 9 formed near the exitfor the heating fluid 1 of the outer cylinder 10 to expand. In thisexample, by virtue of the presence of the unwelded portion 20 betweenthe second baffle plate 8 and the inner cylinder 6, the outer cylinder10 is capable of undergoing a smooth thermal expansion via thecorrugated portion 9.

The reason for positioning the corrugated portion 9 near the exit forthe heating fluid 1 is to reduce the influence of the heating fluid 1 onthe corrugated portion 9 as much as possible.

It is to be noted that since a welded portion 19 provides an airtightwelding between the first baffle plate 7 and the inner cylinder 6, thefluid 2 to be heated flowing in through the inlet 12 can securely bedelivered uniformly to parts in the interior of the inner cylinder 6,inhibiting the fluid 2 from passing through the space defined betweenthe inner cylinder 6 and the outer cylinder 10.

Although this heat exchanger is provided with the first baffle plate 7and the second baffle plate 8 in a pair as shown in FIG. 3, the secondbaffle plate 8 may be excluded therefrom. In such a case, the outercylinder 10 is formed integral with the second tank 16.

Although in the embodiment of FIGS. 1 to 4 the high-temperature heatingfluid 1 is passed through the interiors of the flat tubes 3 whilst thefluid 2 to be heated is passed through the outer peripheral sides of theflat tubes 3, the flow paths of the two fluids may be inverted. Morespecifically, as shown in FIG. 5, the fluid 2 to be heated may flow fromleft to right through the interiors of the flat tubes 3 whereas theheating fluid 1 may flow from right to left through the outer peripheralsides of the flat tubes 3, to thereby achieve a heat exchange betweenthe two fluids. In this case, the heating fluid 1 flows in through theinlet 12 on the right and flows out through the outlet 11 on the left.

1. A heat exchanger comprising: a core in the aggregate of a multiplicity of juxtaposed flat tubes, with a heating fluid flowing through one of the inside and the outside of the flat tubes, with a fluid to be heated flowing through the other; a pair of discoidal tube plates including tube insertion apertures to which the flat tubes are joined at their respective opposed ends; an inner cylinder having a rectangular cross-section enclosing the outer periphery of the core except the vicinities of the pair of tube plates; a first baffle plate having a circular periphery fitted to the outer periphery at one end of the inner cylinder, the first baffle plate confronting one of the pair of tube plates; a circular outer cylinder having one end joined to the first baffle plate and the other end joined to a second baffle plate with a circular periphery disposed on the outer periphery at the other end of the inner cylinder or to the other of the pair of tube plates, the outer cylinder including on its outer periphery a corrugated portion that is thermally expandable in the axial direction; and an outlet and an inlet for the fluid to be heated or the heating fluid disposed at the both end portions of the core between the opposed ends of the inner cylinder and the pair of tube plates, wherein a lead-in port and a lead-out port for the heating fluid or the fluid to be heated are connected respectively to the pair of tube plates.
 2. The heat exchanger of claim 1, wherein the second baffle plate having the circular outer periphery is fitted at its rectangular inner periphery to the outer periphery at the other end of the inner cylinder in such a manner as to be slightly displaceable in the axial direction of the inner cylinder confronting the other of the pair of tube plates, wherein the outer cylinder is firmly connected at the other end thereof to the outer periphery of the second baffle plate, wherein the first baffle plate is fitted at its rectangular inner periphery to the outer periphery at one end of the inner cylinder with the first baffle plate being secured to the outer cylinder, and wherein the heat exchanger further comprises a first and a second cylindrical tank bodies whose opposed ends are firmly connected respectively to the tube plates and to the first and the second baffle plates confronting the tube plates. 